JPS5880545A - Method and device for detecting foreign matter - Google Patents

Abstract

PURPOSE:To detect the presence or absence of foreign matter after setting of a reticle in an exposure optical path by retreating a filter and an exposure control means from the optical path when foreign matter is detected and using the light from the light source directly as illuminating light for detection of foreign matter. CONSTITUTION:Light of a mercury arc lamp 1 of a foreign matter detector irradiates the surface of a reticle 7 by passing through a condenser lens 2, a mirror 5 and a condenser lens 6. When foreign matter 11 exists on the surface of the reticle 7, the irradiating light falls onto the matter 11 and generates reflected and scattered light. Therefore, plural pieces of photoelectric detectors 16 are provided on the upper side of the reticle 7. The reflected and scattered light is detected by the detectors 16 and the electric signals corresponding to said light are compared with a set value, whereby the presence of absence of the foreign matter is detected. It is possible to detect the presence or absence of the stuck foreign matter after setting the reticle in the exposure optical path by keeping the photodetectors 16 retreated from the exposure optical path during exposure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting foreign matter adhering to a reticle of a reduction projection type exposure apparatus.

A reduction projection exposure apparatus is an apparatus that transmits light through a reticle, which is a dry plate having a circuit pattern, to reduce and project the circuit pattern onto a photoresist on a wafer. The configuration of the reduction projection type exposure apparatus will be explained based on FIG. 1.

Light from a mercury lamp 1 as a light source passes through a condenser lens 2, an interference filter 3 for monochromatic light, an aperture 4, a mirror 5, and a condenser lens 61, and illuminates a reticle 7, which is a dry plate having a circuit pattern 77A. The circuit pattern 7A is reduced in size by a reduction projection lens 8 and projected onto the photoresist on the wafer 9. At this time, the area exposed at one time is 1 chip.
Since the wafer 9 is moved in the f x and y directions and MyfiT is applied one chip at a time, the entire surface of the wafer 9 is exposed to light.

At this time, if there is a foreign object on the reticle 7,
Since the exposure light is blocked, the exposure light does not reach the area of the projected image of the pattern corresponding to the area to which the foreign matter has adhered, and pinholes are formed at the hind limbs of the wafer, resulting in the wafer being defective. Furthermore, since each chip portion of the wafer is automatically and continuously exposed, if foreign matter is overlooked, all chips will be defective. Therefore, we constantly inspect the reticle for foreign matter,
If foreign matter adheres during exposure, it is desirable to immediately issue an alarm, stop the exposure, and replace the reticle.

As a conventional foreign matter detection device of this type, there is a foreign matter detection device employed in a moving small projection type automatic mask aligner "DsW" manufactured by GCA of the United States. The main features of this device are shown in Figure 2.
0 As is clear from FIG. 2, a foreign object 11 on the reticle 7
Detection of the presence or absence of the reticle 7 is performed while the reticle 7 is being carried into the exposure optical path. That is, a laser oscillator 12 is placed 1d above the path for carrying in the reticle 7, and a condensing lens 13 focuses the laser beam onto the surface of the reticle 7 into which it is carried.

When the reticle 7 with the foreign object 11 attached thereto is carried in and the foreign object 11 comes directly under the laser focal point, the laser light is reflected by the foreign object and scattered. A lens 14 and a light-receiving element 15 are provided around the condensing point, and the photoelectric light receiving element 15 receives the scattered light, and a detector (not shown) detects the presence or absence of foreign matter based on the distance from the photoelectric light receiving element 15. Display the judgment.

Since the above-mentioned foreign object inspection apparatus performs the inspection during the reticle being carried in, it is not possible to detect foreign objects after the reticle is set in the exposure optical path. However, since there is a possibility that foreign matter may adhere to the reticle even during exposure, there is a need for a foreign matter detection device that can detect the presence or absence of foreign matter after the reticle is set on the exposure optical path.

It is an object of the present invention to overcome the above-mentioned drawbacks of the prior art. # is provided in Tru.

The foreign object detection method and apparatus according to the present invention filter light from a light source to monochromatic light and reduce the amount of light to one level, illuminate a reticle with a circuit pattern, and image the circuit pattern on the photoresist of the wafer. This invention relates to a method and apparatus for detecting a foreign object on a reticle in a reduction projection type exposure apparatus that projects a reduced image.The method for detecting a foreign object according to the present invention, when detecting a foreign object, removes the filter and the optical coupling means from the optical path. After moving out, the source from the light source is used as illumination light for foreign object detection, the reticle surface is irradiated with the illumination light, the reflected and scattered light from the reticle surface is received by a photoelectric receiving element, and the light is emitted from the element. This method is characterized by determining the presence or absence of foreign matter based on the output of.

Further, the foreign object detection device according to the present invention removes the filter and the light amount adjusting means from the optical path when detecting a foreign object, and uses the light from the light source as it is as illumination light for foreign object detection, so that the illumination light illuminates the surface of the reticle. A light shielding plate having a light-transmitting means that partially transmits the illumination light is provided on the optical path leading to the illumination light, and the reticle surface is partially irradiated with the illumination light, and the irradiated portion is moved to the entire surface of the reticle. providing a scanning means for a light-shielding plate, which is directed toward the irradiated portion and moves with the movement of the irradiated portion;
This apparatus is characterized by being provided with a plurality of photoelectric light receiving elements that receive reflected and scattered light from the reticle surface, and means for determining and displaying the presence or absence of foreign matter based on the output from the elements.

In a preferred embodiment of the foreign object detection device according to the present invention,
The light transmitting means is a pinhole or a slit.

In another preferred embodiment of the foreign object detection device according to the present invention, the light transmitting means is a pinhole or a slit fitted with a lens, and the lens focuses the transmitted light on the front or back surface of the reticle. be. Furthermore, in a more preferred embodiment, the light shielding plate is movable up and down by a width corresponding to the thickness of the reticle.

In another embodiment, the optical bone optical element has a lens, a pinhole plate, or a slit plate at its tip.

Next, first, the method of the present invention will be explained based on FIG.

FIG. 3 shows only the portion from the mercury lamp 1 to the reticle 7 of a reduction projection type coalescing device similar to that shown in FIG. The light from the mercury lamp 1 is used as it is as the illumination light for foreign object detection. That is, in this side illumination device, the reticle 7 is irradiated with light from the mercury lamp 1 for exposure, but the exposure light is made into monochromatic light by the interference filter 3, and the light amount χ is adjusted by the diaphragm 4. The strength is extremely weak. Therefore, when detecting a foreign object, the interference filter 3 is moved out of the optical path as shown by the arrow, and the aperture 4 is
Y Make sure to open the mercury lamp 1 sufficiently so as not to block the optical path.
Use the light as is.

The light from the mercury lamp 1 passes through a condenser lens 2, a mirror 5, and a condenser lens 6 and illuminates the reticle 7 surface. If a foreign object 11 exists on the surface of the reticle 7, the irradiated light hits the foreign object 11 and generates reflected and scattered light. Therefore, a plurality of photoelectric light receiving elements 16 are provided above the reticle 7 so as to face the illumination surface of the reticle, and the reflected and scattered light is received by the element 164C, thereby obtaining an output electric signal corresponding to the amount of light received. By comparing this output with the set value using a detector (not shown), it is possible to eliminate foreign particles.
) Detect fi absence. The photoelectric light receiving element 16 obstructs the exposure optical path.

Either it must be installed in a location where there is no foreign object, or it must be moved out of the exposure optical path during full exposure after foreign matter is detected. In addition, when detecting a foreign object, the shutter 10 (
Of course, it is necessary to close the reticle (see Figure 1) or move the reticle (see Fig. 1) out of the exposure optical path.
A exists. Circuit turn 7A O) The thickness is thin,
10 μm or less, generally several μm, and 70) the edges are mainly parallel to the direction of light entry Q) When the reticle 74' is illuminated with illumination light, reflected and scattered light by the circuit nozzle 7A σ) The scattered light is weak (observed as background light. Therefore, the presence or absence of the foreign object 11 can be determined by the single photoelectric receiving element 16Q) and the amount of scattered light received from the foreign object 11 and the circuit (turn). This is done by comparing the amount of scattered light from 7A, that is, the amount of backlight received.The photoelectric light receiving element 16 is used as shown in FIG. If this restriction is not applied, the photoelectric light receiving element 16 will receive a considerable range of background light, and the size of the foreign object that can be detected will generate scattered light that is larger than the amount of background light received (the element is (Can receive light)
It becomes the size. This size is approximately I μm or more in diameter.

If the detection ability is insufficient to detect a foreign substance with a diameter of μm or more, the above-mentioned restriction of the light receiving area of the photoelectric receiving element or restriction of the illumination light irradiation area is carried out. The detection method with such limitations will become clear from the detailed description of the invention that follows.

Next, the apparatus of the present invention will be explained based on FIGS. 4 and 5 showing an embodiment. The apparatus of this embodiment is an apparatus that implements the method of the present invention by limiting the irradiation area of the irradiation light. Of course, in this device as well, when detecting a foreign object, the interference filter and the diaphragm are removed from the optical path, and the light from the mercury lamp is used as the illumination light 11#I for detecting the foreign object. The optical path where the illumination light reaches the 7 surfaces of the reticle,
A light-shielding tent having a light-transmitting means that partially transmits illumination light is arranged between the condenser lens 6 and the reticle 7.

The light shielding plate side is supported on one side by a linear guide 19, and is movable parallel to the reticle 7 in one direction of the reticle, for example, the Y direction (indicated by an arrow 21), and is further provided with a light transmitting means so that it can be moved out of the exposure optical path. In the device shown in FIG. 4, a light-transmitting means is provided in which a cylindrical lens 23Y is fitted in a slit n that is perpendicular to the movement direction 21 on the light-shielding plate side and that exceeds the width of the reticle 7. The cylindrical lens B is designed to focus the transmitted light onto the front or back surface of the reticle 7. In the apparatus shown in FIG. 5, the light is focused on the surface of the reticle 7.

The band-shaped light on the surface of the reticle 7, which is focused by the cylindrical lens, is indicated by the symbol S.

In addition, on the lower surface of the light-shielding tentative title, a plurality of photoelectric light receiving elements 16 are arranged toward the illuminated part of the reticle 7 by a sleeve 22 or a sill.
is the installation. In addition, although not shown in the figure, an electrical signal from the light-generating light-receiving element 16 is input to these devices 5, and the presence or absence of a foreign object is detected by comparing the input value with a set value. A container is provided.

In the apparatus shown in FIG. 4, the reticle 7 is irradiated with a light beam having the width of the slit for 15 minutes at each moving position on the light shielding plate side. Therefore, the scattered light reflected on the circuit pattern, that is, the background light, is significantly reduced, and - photoelectric receiving elements 1
6, the photoelectricity of the background light received is reduced. Therefore, when a foreign object is present, the presence or absence of the foreign object can be detected even if the intensity of the light scattered by the foreign object is small, that is, even if the size of the foreign object is small. In addition, the light shielding plate 20Y,
By moving one way in the direction 2], the entire surface of the reticle 7 can be scanned, and the presence or absence of foreign matter □ and Qi can be detected over the entire surface. 1 When using this device, it is possible to completely detect foreign matter of about 1 μm or more, although it depends on the width of the slit 4 and other conditions.

In the apparatus shown in FIG. 5, the reticle 7 is partially irradiated with a narrow region of the band-shaped light U at each moving position on the light-shielding plate side. However, since the band-shaped light is formed by condensing the light beam with a width of 24 Fi slit ρ using a cylindrical lens, the overall light amount for each band is equal to the amount of light transmitted through slit 4 without a lens device. Equally (assuming there is no absorption by the lens, etc.), the illuminance of each band is greater than the illuminance of the irradiation band of the transmitted light when there is no lens. Therefore, the amount of background light received by the photoelectric light receiving element 16 is almost the same as in the case of the device shown in FIG. 4, but if a foreign object is present,
Since the light irradiating the foreign object becomes stronger, the reflected and scattered light becomes stronger, making it possible to detect even smaller foreign objects. With this device, depending on the slit width and other matters,
Foreign matter of approximately 5/Jm or more can be completely detected.

In the apparatus shown in FIG. 5, the eastern position of the cylindrical lens B is the surface of the reticle 7.

In this case, if foreign matter is attached to the surface of the reticle 7,
``Because the foreign object generates more powerful scattered light, it is difficult to remove a minute foreign object, for example, a foreign object of 5 pm or more. Although it can be detected,
When a foreign object is attached to the surface of the reticle 7, the irradiation light is spread out and reflected, the diffused light becomes weaker, and the size of the foreign object that can be detected becomes larger, for example, 10 μm or more.

Therefore, in one embodiment of the apparatus of the present invention, a light shielding plate having a slit with a lens is movable up and down by a width T corresponding to the thickness of the reticle. An example is shown in FIG.

In FIG. 6, the light shielding plate side is supported by a light shielding plate main body 20A that moves along a linear guide 19 by two leaf springs. Further, the light shielding plate side can be moved up and down by a width corresponding to the thickness of the reticle 7 at the location where the plate spring is located by means of an urging means (not shown). The other configuration is the same as the device shown in FIG. FIG. 6 shows a state in which the irradiated light is focused on the back side of the reticle 7 by the cylindrical lens B, and a band-shaped light 5 is formed on the back side.

In this device, when moving the light shielding plate side, if the height of the light shielding plate I is changed in the forward and return trips, minute foreign objects attached to the front and back sides of the reticle 7 can be detected in both directions. be able to. In addition, instead of moving the light shielding plate 21) up and down, it is possible to use two light shielding tentative lenses with different focal positions of the attached cylindrical lens, or to use two light shielding tentative lenses with different focal positions of the attached cylindrical lens. slit 22
A single light-shielding plate may be used.

In the device of the present invention, a circular, rectangular or square hole (pinhole) may be used as the light transmitting means instead of the above-mentioned slit or a slit fitted with a cylindrical lens. When using these holes (pinholes), the foreign matter detection ability can generally be made higher than when using elongated holes (slits), although it depends on the size of the hole. However, the entire surface of the reticle cannot be scanned unless the light shielding plate is moved in the X and Y directions. Of course, use regular lenses. In addition, it is generally possible to reduce the number of photoelectric light-receiving elements installed. The foreign object detection ability is determined by the difference between the amount of background light received by the photoelectric light-receiving element and the amount of reflected and scattered light from the foreign object. Therefore, the foreign object detection ability It is necessary to make the light receiving area as large as possible.In order to reduce the amount of background light to be received, k should be made by narrowing the illumination area in the light receiving area of the photoelectric light receiving element (constant illuminance condition), or narrowing the light receiving area itself. Making the width of the long hole smaller, changing the long hole to a smaller diameter circular hole, square hole, etc., and reducing the diameter as much as possible will help narrow the illuminated area.

On the other hand, this makes the entire reticle scanning operation progressively more troublesome. The use of lenses does not substantially narrow down the illuminated area since the illuminance is high. In addition, narrowing the light area of the ft* receiver element itself can be achieved by providing a lens, slit, or plate dedicated to a pinhole at the tip of the magneto-optical receiver element.〇The amount of reflected and scattered light from foreign objects can be reduced The only way to make it bigger is to increase the intensity of the illumination light. If the light source 111° of the illumination light is made more powerful, the background light will be increased accordingly. However, since the difference in luminous intensity between the reflected and scattered light from the foreign object becomes large, '' is useful for improving the ability to detect foreign objects. In the device of the present invention,
The light source of the exposure device on the main body is used, but in order to increase the luminous intensity, the filter and diaphragm are removed when a foreign object is coughed up. In order to obtain more powerful illumination light, it is necessary to introduce light from another light source. This has the disadvantage of complicating the device. The apparatus of the present invention can exhibit sufficient detection ability through the above-described processing, and in a further preferred embodiment, the detection ability can be further improved by making the illumination light that illuminates the lens more powerful. It is improving your morale.

As described above, when using the method and apparatus of the present invention, it is possible to detect at any time the presence or absence of foreign matter on the reticle after it is attached to the exposure optical path of the reduction projection exposure apparatus. Since the light source of the exposure device is used instead of the reticle, the equipment can be simplified.Moreover, it can improve the detection accuracy, and by performing the test under appropriate conditions, it can detect particles of approximately 5 μm or more that adhere to the front and back surfaces of the reticle. Therefore, the method and apparatus of the present invention can be used to detect foreign objects at any time or intermittently, for example, with respect to the reticle after mounting.
Since the presence or absence of foreign matter can be detected every minute, the risk of producing defective products is significantly reduced, and the added value of the reduction projection exposure apparatus can be greatly improved by the method and apparatus of the present invention.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an example of a reduction projection type exposure device, FIG. 2 is a factor a of an example of a conventional foreign object detection device, FIG. 3 is a principle diagram for explaining the foreign object detection method of the present invention, and FIG. Figure (at,
(b) and FIG.
Front view (Figure b) and side view (Figure 0, but only Figure 5),
6(a) and 6(b) are a front view (a) and a side view (b) of still another embodiment of the device of the present invention. 1... Water lamp, 2.6... Condenser lens, 3.
...Interference filter, 4...Aperture υ, 5...Mira, 7.
...Reticle, 7A...Circuit pattern, 8...Fine'
Small projection lens, 9... Sea urchin eight, 10... Shutter,
11... Foreign matter, 12,15° 16... Light transmissive light receiving element, 19... Kin kite, eggplant... Light shielding plate, n...
Slit, n...Cylindrical lens, see. 5... band-shaped light, ah... leaf spring. 1st section Figure 4 (a) j14 cause (b) Figure 5 (Φ 5IIA (b)

Claims (1)

[Claims] 1. Reduction in which the light from the light source is filtered into monochromatic light and the sight is adjusted to illuminate the reticle having the circuit pattern, and the circuit pattern image is reduced and projected onto the photoresist of the wafer. In a method for detecting a foreign object on a reticle in a projection exposure apparatus, when detecting a foreign object, the filter and the light adjusting means are removed from the optical path, and the light from the light source is used as illumination light for detecting the foreign object. , the reticle surface is irradiated with the illumination light, the reflected and scattered light from the reticle surface is received by a photoelectric receiving element, and the presence or absence of a foreign object is determined based on the output from the element. Detection method. 2. The light emitted from the light source is made into monochromatic light by a filter, and the amount of light is adjusted to illuminate a reticle having a circuit pattern, and the circuit pattern image is reduced and projected onto the photoresist of the wafer. In a foreign object detection device on a reticle, when foreign object 2.1 is detected, the filter and light amount adjustment means are removed from the optical path, and the light from the light source is used as it is as illumination light for foreign object detection, and the illumination light is directed to the reticle surface. A light shielding plate having a light-transmitting means that partially transmits the illumination light is provided on the optical path leading to the illumination light, and the reticle surface is partially irradiated with the illumination light, and
a light shielding plate scanning means for moving the irradiated portion over the entire surface of the reticle; a plurality of photoelectric light receiving elements directed toward the irradiated portion and moved along with the movement of the irradiated portion; a plurality of photoelectric light receiving elements that receive reflected and scattered light from the reticle surface; and means for determining and displaying the presence or absence of a foreign object based on the output from the element. 3. The foreign object detection device according to claim 2, wherein the light transmitting means is a pinhole or an L slit. 4. Claim 2, wherein the light transmitting means is a pinhole or a slit fitted with a lens, and the lens focuses transmitted light on the front or back surface of the reticle.
Foreign object detection device. 5. The foreign object detection device according to claim 4, wherein the light shielding plate is movable up and down with a width corresponding to the thickness of the reticle. 6. The foreign object detection device according to claim 3, 4, or 5, wherein the photoelectric light receiving element has a lens, a pinhole plate, or a slit plate at its tip.